Drilling jars are typically installed into a drill string that normally incorporates a drill bit at the bottom, various drill collars thereabove, stabilizers as necessary, and a plurality of drill pipe to extend from the kelly at the derrick to the bottom of the borehole. A drilling jar is included into the drill string to enable an operator to deliver a jar or jolt to the drill string whenever the drill string becomes stuck during drilling operations. In addition, the drilling jar may be used to apply an impact to an object that is stuck in the borehole. This impact should knock the stuck object loose, allowing it to be retrieved from the borehole.
Under normal drilling operations, conventional drilling jars perform satisfactorily. Some types of mechanical jars can be adjusted downhole to increase the triggering force, thus the intensity of the blow, by applying right hand torque when stuck. Under certain drilling conditions, if too much right hand torque is applied and cannot be released because of the configuration of the well, it becomes difficult or impossible for the drilling jar to trigger and deliver a blow in either the upward or downward direction.
During drilling operations, the drill bit has a tendency to "walk right" producing a corkscrew configuration of the bore hole. This configuration is more pronounced during fast drilling. Moreover, in directional drilling, the formation discontinuities and deviation procedures add "dog legs" to the bore hole. The corkscrew configuration and dog legs trap the right hand torque applied for drilling, making the jar triggering action more difficult or even impossible.
The method normally used to overcome this trapped right hand torque is to work left hand torque down the drill string to the drilling jar, approximately one round at a time. This method is very time consuming, thus costly. In directional drilling wells, the corkscrew configuration and dog legs present in the bore hole may impede the left hand torque from reaching the jar. Thus, right hand torque remains trapped in the tool. The jar can not be triggered and cannot provide an upward or downward hammering action. This problem is more acute for high angle holes and any directional well drilled at a fast rate of penetration.